Single sideband transceivers attempt to reject an undesirable sideband by cancellation techniques carried out in an image product mixer therein. When single sideband transceivers can be constructed from a collection of discrete components, the ability to select and match these components to minimize the undesirable image product allows strong image product rejection to be achieved. However, in high-volume products, where cost is usually a key factor to be minimized, the cost of labor to accomplish this is usually prohibitive. This is certainly the case with consumer cordless phones, which have both a handset and a base transceiver requiring calibration of two transmitter-receiver pairs to operate properly.
Currently, cordless phone transceivers use integrated circuit devices with minimal or no calibration adjustment capability possible. Commonly used devices, such as the AD 6190 and the MAXIM 2420, provide no means for adjustment. Mismatches in phase and amplitude from polyphase integrated circuit filters often used therein results in only approximately 35 dB of cancellation or unwanted image product rejection. The situation may be exacerbated if two cordless phones are operated close to one another. In this situation, the environment may give rise to a problem in that both cordless phones may be using a communications frequency that falls into the undesired image product. This condition generates crosstalk and interference between the two cordless phones that may degrade or disrupt communication. This degradation is usually amplified if at least one of the phones is far from its base and therefore is operating with minimal signal strength.
Accordingly, what is needed in the art is way to calibrate single sideband transceivers employed in cordless phones efficiently and effectively.